1. Field of the Invention
The present invention pertains to the operation of a fuel processor and, more particularly, to the identification of a firstout shutdown condition in a fuel processor.
2. Description of the Related Art
Fuel cell technology is an alternative energy source for more conventional energy sources employing the combustion of fossil fuels. A fuel cell typically produces electricity, water, and heat from a fuel and oxygen. More particularly, fuel cells provide electricity from chemical oxidation-reduction reactions and possess significant advantages over other forms of power generation in terms of cleanliness and efficiency. Typically, fuel cells employ hydrogen as the fuel and oxygen as the oxidizing agent. The power generation is proportional to the consumption rate of the reactants.
A significant disadvantage which inhibits the wider use of fuel cells is the lack of a widespread hydrogen infrastructure. Hydrogen has a relatively low volumetric energy density and is more difficult to store and transport than the hydrocarbon fuels currently used in most power generation systems. One way to overcome this difficulty is the use of “fuel processors” or “reformers” to convert the hydrocarbons to a hydrogen rich gas stream which can be used as a feed for fuel cells. Hydrocarbon-based fuels, such as natural gas, LPG, gasoline, and diesel, require conversion processes to be used as fuel sources for most fuel cells. Current art uses multi-step processes combining an initial conversion process with several clean-up processes. The initial process is most often steam reforming (“SR”), autothermal reforming (“ATR”), catalytic partial oxidation (“CPOX”), or non-catalytic partial oxidation (“POX”). The clean-up processes are usually comprised of a combination of desulfurization, high temperature water-gas shift, low temperature water-gas shift, selective CO oxidation, or selective CO methanation. Alternative processes include hydrogen selective membrane reactors and filters.
Thus, many types of fuels can be used, some of them hybrids with fossil fuels, but the ideal fuel is hydrogen. If the fuel is, for instance, hydrogen, then the combustion is very clean and, as a practical matter, only the water is left after the dissipation and/or consumption of the heat and the consumption of the electricity. Most readily available fuels (e.g., natural gas, propane and gasoline) and even the less common ones (e.g., methanol and ethanol) include hydrogen in their molecular structure. Some fuel cell implementations therefore employ a “fuel processor” that processes a particular fuel to produce a relatively pure hydrogen stream used to fuel the fuel cell.
Fuel processor designs are typically highly involved. Typically, a substantial number of subsystems interact in a complicated manner to produce the hydrogen for the fuel cell. For instance, a fuel processor might mix water, air, and a fuel, and reform the mixture. Thus, the fuel processor may have a separate subsystems directed to delivering the water, air, and fuel to a mixing subsystem to produce the process feed gas. Quantities, pressures, and temperatures of the water, air, fuel, and process feed gas are controlled during the mixing process to achieve a desired composition for the process feed gas and prepare it for reforming. The mixing subsystem then delivers the process feed gas to a reforming subsystem in a controlled manner. The reforming process itself constitutes several smaller processes, each of which may occur at a different temperature and pressure.
Any one of these quantities, pressures, temperatures, etc. may generate an error condition in the operation of the fuel processor for a host of reasons. Some of these error conditions may warrant shutting down the fuel processor until it can be corrected, i.e., a “shutdown.” A fuel processor typically includes a control system that monitors these types of parameters for error conditions and shuts down the fuel processor. Upon shutdown, an operator or a maintenance technician ascertains the cause of the shutdown, corrects the problem, and then the fuel processor is brought back into operation.
The involved design of the fuel processor frequently spawns a difficult problem in this context. A shutdown is usually initiated by a single shutdown error condition. This condition is referred to as the “firstout.” However, the effects of the firstout typically propagate through the fuel processor very quickly, triggering other shutdown error conditions. Consequently, by the time the fuel processor is shut down, there may be very many shutdown error conditions present. The operator or maintenance technician must then wade through all these error to determine which was the firstout in order to correct the problem. The process of the determining which of the shutdown error conditions was the first out can be long and costly.
The present invention is directed to resolving, or at least reducing, at least one of the problems mentioned above.